Too intense? Kristin Stewart and Robert Pattinson as Bella and Edward in The Twilight Saga: Breaking Dawn Part Two.
Photograph: Allstar/Summit Entertainment

We all love a bad guy, right? One of my earliest love interests was Heathcliff from Wuthering Heights. I seriously thought I could change that guy – surely he just was misunderstood? I figured that his broody, moody ways meant he’d be an intense and passionate lover – and that being with someone nice and understanding like me would bring out their softer side. I don’t think I was alone in thinking that.

In many teen and YA books, bad boy characters work because we can see that they have the capacity to change. Characters like Jace Wayland in Cassandra Clare’s Mortal Instruments or Snape in Harry Potter are dark and twisted, but we can see the light deep in their souls. There is hope. We can champion these figures and like them all the more for their flaws. Hey, I’m a Snape girl all the way – he always was my favourite character.

But these are not the only “bad boys” we are encountering in books for young people. We also have to consider books that have sprung up in the wake of Twilight, portraying more intense relationships: characters who are darker, who can make you feel frightened. A good example of this can be found in Hush, Hushby Becca Fitzpatrick. Books like these can respond to our desire to explore intense, complex relationships. But transposed to the real world, these situations are dangerous, and an open conversation, reminding young people of that, should never be far away.

It can be difficult to explore toxic love in contemporary novels: you are reflecting the true nature and experience of being with – or sometimes, being – a troubled person. Yes, sometimes they do work out – but most often they don’t. They frequently lead to abuse. According to an NSPCC report, one in five teenagers has been physically abused by their boyfriend or girlfriend. In Crush I wanted to show this – that controlling love can turn very bad – and I didn’t want to romanticise it.

I think I’ve always wanted to write Crush. I remembering watching my favourite film, Oliver, and being drawn to the painful character of Nancy. I listened to her warble “As long as he needs me” and felt a sense of injustice. Why was this woman so attracted to the brutal and controlling Bill Sykes? As I watched the tragic scene on the bridge unfold, I would sob every time – in frustration as much as sorrow. She should never have been with him. Their relationship shouldn’t have got that far.

I knew then that toxic love could never end well.

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As a teenager, I lost my best friend to her boyfriend of the time. He was controlling and manipulative. I saw her change from a loud, confident girl into a quiet, submissive character. She slipped into his shadow. She wasn’t the only one. Another girl in my year dated a violent bully. He wasn’t like that at the beginning, of course. He was charming and kind; he made her feel special. At the age of sixteen, she thought that love was having a boy tell you what to do and how to do it, and she put up with the slaps because she thought she deserved them. He had made her feel that way.

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Throughout my life I have met people in controlling relationships. I have seen friends change who they are in order to please their partner. And please don’t think I’m saying this is uniquely an issue of men dominating women. Women can be toxic too. I have witnessed many men who have been controlled and belittled by their partners and find it difficult to talk about. In addition, one of my male relatives was in a same sex relationship that turned violent and it wasn’t until he broke away that he realised how isolated he had become. Looking from the outside in, he barely recognised himself.

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More recently, while working in schools, I’ve seen the impact that toxic love can have on young people. I saw a popular and bright 15-year-old fall in love with a charismatic older boy. I saw her change quickly into a defensive and confused girl, trying to hide the bruises on her arms, falling behind with her school work and, finally, running away from home. She told us again and again that we didn’t understand, that her boyfriend loved her, that she was fine. The thing was, we did understand; we understood only too well. And we knew this wasn’t love – we could tell by the scratch marks around her neck.

Toxic love is not a subject that should be ignored, and it is great that it has been covered in books for young people, such as Loving Danny by Hilary Freeman and He’s After Me by Chris Higgins. Of course, these toxic characters aren’t all bad. In Crush, my character Anna is drawn into a controlling and damaging relationship with the enigmatic Will. But Will has his own demons. There are always reasons why someone’s behaviours are controlling and abusive – there is always a history behind them. And this is what needs to be explored more. Early intervention, addressing the problems sooner rather than later, is needed to prevent these unhealthy behaviours.

If not, our toxic young heroes could become future controlling bosses, angry parents or abusive partners.